Fourth generation (4G) cellular networks employing newer radio access technology (RAT) systems that implement the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) and LTE Advanced standards, are rapidly being developed and deployed within the United States and abroad. These deployments are being made in attempt to accommodate for an ever-increasing demand for Internet Protocol (IP) data communications, which is a natural consequence of the exponential growth of the personal computing device market, in conjunction with the increasing popularity of numerous social networking and media content provider services that are available over the Internet.
Networks utilizing these newer RATs often support significantly higher data rate throughputs, as compared to the throughput capabilities of preexisting cellular networks employing legacy RATs, such as third generation (3G) Universal Mobile Telecommunications System (UMTS)/High Speed Packet Access (HSPA) systems, 3G Code Division Multiple Access (CDMA) 2000/1× Evolution-Data Only (1× or EV-DO) systems, as well as second generation (2G) Global System for Mobile Communications (GSM)/Enhanced Data Rate for GSM Evolution (EDGE) systems.
In some 4G deployments, LTE and other newer RATs may not be adapted to fully support certain services that are supported by predecessor 2G and 3G legacy networks. Accordingly, many modern LTE networks are co-deployed within overlapping network topologies, alongside of other legacy networks. In these heterogeneous network environments, consumer wireless communication devices can transition between different RATs as communications services and/or network coverage may require.
For example, some LTE networks may not be capable of supporting voice calls via voice over LTE (VoLTE). Accordingly, when a wireless communication device receives or initiates a voice call communication, while connected to a 4G network that only supports IP data transfers, but not voice calls, the wireless communication device can perform a circuit switched fallback (CSFB) procedure in order to transition back to to a 2G or 3G legacy network that supports voice calls. Further, when a wireless communication device that is engaged in a VoLTE communication session exits or roams beyond a corresponding LTE coverage area, the device may perform one or more single radio voice call continuity (SRVCC) functions to effectuate a smooth transition back to an available 2G or 3G legacy network.
Alternatively, when a wireless communication device attempts to send or receive IP data, while connected to a 2G or a 3G legacy network that is not capable of, or is poorly equipped for, supporting the IP data transfer session's bandwidth requirement, the wireless communication device can perform a forward handover to a more capable 4G network. By way of example, this scenario may occur at a time when an LTE network becomes available to and/or is detected by the wireless communication device during the current packet-based communication session.
Additionally, when a wireless communication device transitions between and amongst different geographic regions associated with multiple, different cellular network providers that may employ a variety of proprietary 2G, 3G, and/or 4G RATs, the wireless communication device needs to identify available communications services to determine a most appropriate network to attach to, or camp on. By establishing an appropriate network attachment, the wireless communication device can conduct a voice call and/or an IP data transfer session via a corresponding circuit switched (CS) or a packet switched (PS) communication, or both. To effectuate network selection or reselection procedures while roaming, the 3GPP has standardized use of a public land mobile network (PLMN) list, and the 3GPP2 standards body has similarly implemented a preferred roaming list (PRL). A wireless communication device can employ a PLMN list or a PRL to readily identify which available cellular networks are roaming partners of a particular cellular network provider to which a user of the wireless communication device is subscribed, i.e., its carrier network.
At a time when a wireless communication device is powered up or is otherwise attempting an initial connection to an available network, or during any of the above described network handover scenarios, the wireless communication device may attempt to perform a full network scan over various assigned RAT frequency bands that may be allocated to its carrier, its carrier's roaming partner(s), and/or one or more unaffiliated network service providers. These extensive network searches can take a considerable amount of time and may only be practically feasible when a wireless device is first powered on or is roaming in an unfamiliar geographic region, as indicated by the geographic index information stored in the wireless communication device's PLMN list or the PRL.
For example, in a scenario where a 4G multi-mode wireless communication device attempts to locate an available LTE network, the device may perform an initial system scan over various known LTE frequency bands, e.g., bands within the 700 MHz, 1700 MHz and 2100 MHz mobile spectrum, to try tune to an available LTE network. However, when no corresponding LTE networks are detected during a first portion of the scan, the device may subsequently attempt to scan various known 3G legacy frequency bands, e.g., bands within the 850 MHz and 1900 MHz mobile spectrum, to attempt to tune to an available HSPA+ or EV-DO network during a second portion of the scan. Likewise, if the 3G legacy scan were also unsuccessful, the device may attempt a scan of various 2G legacy frequency bands to try to tune to an available EDGE network during a third portion of the scan.
In other scenarios, where a wireless communications device has recently camped on one or more wireless networks within a certain geographic area, historical network information about these known systems can be stored within a temporary memory or cache storage area of the wireless communication device known as a most recently used list (an MRU or MRUL). The device's MRUL may comprise a short listing of one or more network systems to which the wireless communication device was most recently attached. The MRUL can allow the device to readily identify familiar networks during a short-listed frequency scan procedure.
However, most MRULs are carrier-generic. As such, these lists often indiscriminately maintain identifying information about each one of a limited number networks that a wireless communication device has previously camped on. For instance, an MRUL may include only basic identifying information about a limited number of networks that include one or more preferred roaming partner networks. Each time the wireless communication device attaches to a new network, it may update the MRUL by adding information about the latest network attachment to the MRUL. At the same time the latest network attachment information is added to the MRUL, the last-used network system (i.e., the system at the end of a full MRUL) may be systematically removed from the MRUL, or pushed out of the MRUL in order to make room for the new entry.
As MRULs are often indiscriminately maintained, they can include network system information pertaining to both a home carrier network and multiple roaming networks, which are collectively associated with multiple, differing frequency spectra. For instance, an MRUL may include information associated with diversified frequency spectra for multiple carriers; this diversified composite would not facilitate a quick scan of a relatively small number of frequency resources associated with a designated carrier, prior to resorting to extended frequency band scans for multiple roaming networks. Consequently, MRULs often inefficiently include some of the very same frequency and channel information that exists in a device's PLMN list or PRL. Not only can this result in redundant frequency band searches, but it may significantly increase the timing requirements associated with performing compact MRUL scans.
Accordingly, there remains a need for generating and maintaining an MRUL that better discriminates amongst historical network attachment information of a wireless communication device. It would be advantageous if a wireless communication device could utilize its MRUL to readily identify available wireless networks associated with its carrier during network reselection events to avoid wasting valuable device resources, i.e., by performing redundant and/or unnecessary frequency scans outside of its carrier's allocated frequency spectra.